1. Field of the Invention
The present invention relates to a digital rights management method and apparatus, and more particularly, to a method and device for moving a rights object (RO) between devices and a method and device for using a content object based on the moving method and device.
2. Description of the Related Art
Recently, digital rights management (DRM) has been actively researched and developed. Commercial services using DRM have already been used or will be used. DRM needs to be used because of the following various characteristics of digital content.
Unlike analog data, digital content can be copied without loss and can be easily reused, processed, and distributed, and only a small amount of cost is needed to copy and distribute the digital content. However, a large amount of cost, labor, and time are needed to produce the digital content. Thus, when the digital content is copied and distributed without permission, a producer of the digital content may lose profit, and enthusiasm for creation may be discouraged. As a result, development of digital content business may be hampered.
There were several efforts to protect digital content. Conventionally, digital content protection has been concentrated on preventing non-permitted access to digital content, permitting only people who have paid charges to access the digital content. Thus, people who have paid charges for the digital content are allowed to access and decrypt digital content while people who have not paid charges are not allowed to access and decrypt digital content. However, when a person who has paid charges intentionally distributes the digital content to other people, the other people can use the digital content without paying charges.
To solve this program, DRM was introduced. In DRM, anyone is allowed to freely access encoded digital content, but a license, referred to as a rights object, is needed to decode and execute the digital content. Accordingly, the digital content can be more effectively protected by using DRM.
FIG. 1 is a diagram illustrating typical digital rights management (DRM). DRM generally involves handling content that is protected by being encrypted or scrambled and handling licenses allowing access to such encrypted content.
FIG. 1 illustrates a plurality of devices, e.g. device A (110) and device B (150), which desire to access encrypted content, a content provider 120 which provides content, a rights object (RO) issuer 130 which issues an RO containing a license for executing content, and a certificate authority 140.
The device A (110) obtains desired content from the content provider 120, wherein the desired content is encrypted content. The device A (110) purchases an RO containing a license for using the encrypted content from the RO issuer 130. Thereafter, the device A (110) can use the encrypted content using the purchased RO.
Encrypted content can be freely circulated or distributed. Therefore, the device A (110) can freely transmit encrypted content to device B (150). In order for the device B (150) to play back the encrypted content transmitted by the device A (110), the device B (150) needs an RO which can be purchased from the RO issuer 130.
The certificate authority 140 issues a certificate signed with a message specifying an identifier of a device whose public key has been identified, a certificate number, the name of the certificate authority 140, and the expiration dates of the public key of the device and the certificate. The devices, e.g. device A (110) and device B (150), can determine whether devices currently communicating with them are legitimate devices by referencing certificates of the devices issued by the certificate authority 140. The devices may be equipped with certificates issued by the certificate authority 140 when manufacturing the devices A (110) and B (150). The devices A (110) and B (150) may have their certificates reissued by the certificate authority 140 when their certificates expire.
Certificates issued to devices by the certificate authority 140 are signed with a private key of the certificate authority 140. Thus, devices can examine certificates issued to other devices which are currently communicating with them using their public keys. Certificates issued by the certificate authority 140 may be stored in places that are easily accessible by devices or may be stored in the devices.
FIG. 1 illustrates that an RO and encrypted content are directly transmitted between the device A (110) and the device B (150). However, recently, methods of transmitting an RO and encrypted content between devices via a portable storage device have been developed.
In such portable storage device-based methods, a device can store an RO in a portable storage device and can use encrypted content using the RO stored in the portable storage device. Therefore, DRM may also be applied to communication between a device and a portable storage device, which is illustrated in FIG. 2.
FIG. 2 is a diagram illustrating DRM for communication between a portable storage device and a device. Referring to FIG. 2, a device A (210) can obtain encrypted content from a content provider 220. The encrypted content is content protected through DRM. To use, e.g. to play, the encrypted content, a Rights Object (RO) for the encrypted content is needed. An RO contains a definition of a right, a right to content, and constraints to the right and may further include a right to the RO itself. An example of the right to the content may be a playback, or other rights known in the art. Examples of the constraints may be the number of playbacks, a playback time, and a playback duration, or other constraint known in the art. An example of the right to the RO may be a move or a copy, or other right to the RO known in the art. In other words, an RO containing a right to move may be moved to another device or a secure multi media card (MMC). An RO containing a right to copy may be copied to another device or a secure MMC. When the RO is moved, the original RO before the move is deactivated (i.e., the RO itself is deleted or a right contained in the RO is deleted). However, when the RO is copied, the original RO may be used in an activated state even after the copy.
Referring to FIG. 2, the device A (210) receives encrypted content from the content provider 220 and issues a request for an RO to an RO issuer 230 to obtain a right to play back the encrypted content. When receiving the RO from the RO issuer 230, the device A (210) can play back the encrypted content using the RO. The device A (210) may transmit the RO to the device B (250), which possesses the encrypted content, using a portable storage device. The portable storage device may be a secure multimedia card 260 having a DRM function. In this case, the device A (210) and the secure multimedia card 260 authenticate each other, and the device A (210) transmits the RO to the secure multimedia card 260. Then, in order to play back the encrypted content, the device A (210) may issue a request for the RO to the secure multimedia card 260 and receive a right to play back the encrypted content, i.e., a content encryption key, from the secure multimedia card 260 in return. The secure multimedia card 260 and the device B (250) authenticate each other. Then, the secure multimedia card 260 may transmit the RO to the device B (250) or may allow the device B (250) to play back the encrypted content.
As described above, in conventional DRM methods, an RO and a content object are transmitted from a service provider to arbitrary devices. Therefore, in order for a device to use a content object, the device must have both the content object and an RO corresponding to the content object. In addition, a consumed RO cannot be exposed outside the device where the consumed RO is currently located, with current state information of the consumed RO kept intact. Therefore, a user may not be able to properly maintain the RO for which the user has already made payment when purchasing a new device or replacing the device with another device.